The typical hard disk drive includes a head disk assembly (HDA) and a printed circuit board (PCB) attached to a disk drive base of the HDA. The head disk assembly includes at least one disk (such as a magnetic disk, magneto-optical disk, or optical disk), a spindle motor for rotating the disk, and a head stack assembly (HSA). The printed circuit board assembly includes electronics and firmware for controlling the rotation of the spindle and for controlling the position of the HSA, and for providing a data transfer channel between the disk drive and its host.
The spindle typically includes a rotor including one or more rotor magnets and a rotating hub on which disks are mounted and clamped, and a stator. If more than one disk is mounted on the hub, the disks are typically separated by spacer rings that are mounted on the hub between the disks. Various coils of the stator are selectively energized to form an electromagnetic field that pulls/pushes on the rotor magnet(s), thereby rotating the hub. Rotation of the spindle hub results in rotation of the mounted disks.
The head stack assembly typically includes an actuator, at least one head gimbal assembly (HGA), and a flex cable assembly. Each HGA includes a head for reading and writing data from and to the disk. In magnetic recording applications, the head typically includes an air bearing slider and a magnetic transducer that comprises a writer and a read element. The magnetic transducer's writer may be of a longitudinal or perpendicular design, and the read element of the magnetic transducer may be inductive or magnetoresistive. In optical and magneto-optical recording applications, the head may include a mirror and an objective lens for focusing laser light on to an adjacent disk surface.
During operation of the disk drive, the actuator must rotate to position the HGAs adjacent desired information tracks on the disk. The actuator includes a pivot-bearing cartridge to facilitate such rotational positioning. The pivot-bearing cartridge fits into a bore in the body of the actuator. One or more actuator arms extend from the actuator body. An actuator coil is supported by the actuator body, and is disposed opposite the actuator arms. The actuator coil is configured to interact with one or more fixed magnets in the HDA, typically a pair, to form a voice coil motor. The printed circuit board assembly provides and controls an electrical current that passes through the actuator coil and results in a torque being applied to the actuator. Because of the narrowness of contemporary information tracks and the speed with which the disks are rotated, the heads must be actively positioned (by the actuator) with acceptable bandwidth to quickly and reliably read and write data.
The head is adhered to a suspension assembly that includes a gimbal, load beam, bend region, and swage plate. The bend region of the suspension assembly has important mechanical properties that must be carefully controlled. For example, in a vertical direction the bend region serves as a spring (that is significantly more compliant than the load beam), to preload the head against the surface of the disk, yet allow the head (and more rigid load) beam to follow vertical undulation of the disk as it rotates. However, in a horizontal direction the bend region must be stiff so that the actuator can accurately position the load beam and head adjacent desired tracks of information on the disk. During operation, the head is typically separated from the disk by an extremely thin layer of ambient gas known as the “air bearing.” This air bearing separation may enable the disk drive to function reliably for an acceptable period of time without damage or unacceptable wear to the disk or head from friction and rubbing contact.
However, high rotational accelerations of the actuator and externally applied mechanical shocks may excite undesired vibration modes of the suspension assembly. Such ringing of the suspension assembly may interfere with actuator control of the position of the head, adversely affecting operation of the disk drive, and also may cause an undesired or unacceptable amount of contact between the head and the disk—which, in turn, may lead to tribological problems and increased possibility of head crash and head-disk interface unreliability.
One method known in the art to control suspension assembly vibration in information storage devices is to adhere a constrained-layer damper to the suspension assembly. However, certain disadvantages have also been associated with adhering a constrained-layer damper to the suspension assembly. For example, there has typically been a large engineering uncertainty in the relative position of the constrained-layer damper during manufacture of the HGA. If a portion of the constrained-layer damper is adhered to the bend region of the suspension assembly, then the positional uncertainty of the constrained-layer damper can undesirably variably affect the important mechanical properties of the bend region. However, if the constrained-layer damper is alternatively positioned entirely on the more rigid load beam, then the strain energy imparted to the constrained-layer damper may be insufficient to adequately control suspension assembly vibration.
Thus, there is a need in the art for an improved method to control suspension assembly vibration in information storage devices.